Not Applicable.
Not Applicable.
Not Applicable.
The present invention relates to anatomical support apparatus and more particularly to a cushion having layers of gel, an open cell panel and a foam base.
Persons requiring the assistance of wheelchairs are at risk for the development of pressure sores from sitting on wheelchair seats or cushions. Pressure sore development is clinically termed decubitus ulceration. Decubitus ulceration arises primarily from prolonged exposure to unacceptably high pressure levels and the subsequent loss of adequate blood flow to the affected tissues. Secondly, decubitus ulceration results from any internal horizontal or tangential forces imparted deep within the tissue layers. This horizontal tearing within the deep tissue layers is commonly known as sheer. It primarily originates along bone-tissue interfaces, or tissue-tissue interfaces (when the tissues are sufficiently dissimilar in elasticity, density or structure). Other factors compound the likelihood of decubitus ulcer development and may additionally impede the healing process. The general healthiness, elasticity and integrity of the patient""s tissue, available natural cushioning, i.e., adipose tissue (fat tissue) surrounding the affected bony protuberances of the seated posture, the average sustained surface temperature of the cushioning device, moisture due to perspiration or incontinence, maintenance requirements of the cushioning device itself, the patient""s cognitive abilities when required to adhere to a regimen of weight shifting and re-positioning themselves on the cushioning device and the attentiveness of caregivers when requiring assistance with these tasks.
Premium cushioning devices are designed to prevent pressure sores and/or to promote healing of pressure sores. The first requisite of a premium cushioning device is to diminish the downward measurable pressure, especially in areas which correspond to the location of bony prominences and thereby maintain healthy circulation. This is primarily achieved through increasing the contacted area via anatomical contouring of the cushioning device. This contouring is the result of the manufactured shaping (unloaded contouring) plus the compression of the cushioning device at loaded equilibrium, i.e., the time required for the cushioning device to undergo no additional compression with respect to time.
Today, computerized pressure mapping systems are widely used in wheelchair assessment clinics. These systems measure pressure between the patient and the surface of the cushioning device and this surface of the cushioning device is commonly referred to as the xe2x80x9cpatient interface.xe2x80x9d This external reading of pressure is an index and used to approximate the actual pressures which lie across the bone-tissue interfaces deep within the body. Pressure sores generally originate deep within the tissue layers along the bony prominences and progress outward to the external epidermis. Clinicians have developed guidelines to model the required indexed pressure readings to prevent the onset of pressure sores. Clinicians have also modeled the required external pressure readings which are required to reestablish the healthy circulation necessary to heal existing pressure sores. The external pressure readings which correspond to the coccyx, the sacrum and the ischial tuberosities (the relatively sharp endings of the posterior pelvis) are the areas most heavily scrutinized during wheelchair seating assessments.
A second requisite for a premium cushioning device is to provide a stable platform to enhance pelvic stability and to improve postural alignment. With time, a patient with poor sitting posture may develop pronounced skeletal deformities. Initially these deformities are reversible and are clinically termed xe2x80x9cflexible,xe2x80x9d such as a xe2x80x9cflexible pelvic obliquity.xe2x80x9d In time, these compromised postures become permanent deformities through the calcification of the affected joints and may lead to additional complications, including circulatory, neurological, respiratory, and physically interfere with daily activities such as eating or transferring from a wheelchair to a bed or toilet. Ideally, for a cushioning device to address this pelvic postural requirement, termed xe2x80x9cpositioning,xe2x80x9d the cushion at loaded equilibrium must have sufficient depth in contouring (manufactured contours plus additional loaded contouring) to anatomically resemble the human sitting regions, which include the underside of the upper and lower thighs. Additional stability is made possible if the pressure relieving media retain a uniform thickness at loaded equilibrium, that is, if they are highly viscous or semi-solid.
Many pressure reduction and positioning cushioning devices have been made available. The less effective and simpler devices are primarily designed to afford some degree of pressure reduction with some level of enhanced comfort. These devices are generally comprised of a single density polyurethane foam encased within a cover and are without any manufactured contours and are referred to as xe2x80x9cplanar seating.xe2x80x9d These devices do not provide a stable or sufficiently contoured loaded interface to assist in achieving or maintaining a more desirable posture. Other more sophisticated versions of the planar cushion utilize multiple layers of different density polyurethane foam with or without additional pressure relieving media encased within a cover. An example of a complex planar cushion may use a gel, either water based, polyurethane or a silicone encased within a thin plastic envelope disposed on top of one or multiple densities of foam. These types of cushions generally provide better pressure reduction than the simpler planar foam cushions with no appreciable improvement in their ability to correct a poor sitting posture. These wheelchair cushions still fall in the general category of comfort cushions and are not prescribed for patients who have a history of pressure sores or who have several factors which place them at high risk for pressure sore development (i.e., poor skin integrity, incontinence, poor nutrition, etc.).
Other types of cushions exist which were primarily designed to deliver high pressure reduction without much regard to their ability to properly position the patient. The best example of this type of cushion is the Roho cushion. The Roho cushion uses a neoprene bladder comprised of interconnected vertical cells encased within a cover. The contained volume of air can flow from one cell to another and is effectively baffled by the use of small port openings. The total vertical loading on this cushion type is primarily deflected via the increased total surface area of affected or contacted cells plus the total internal surface area of the non-contacted cells. However, these cushions require the patient to have the necessary dexterity to adjust the contained volume of air via a supplied pump. Frequently, within six months these cushions require daily adjustment due to ever increasing rates of air loss. Their optimum operating air pressure range is relatively narrow and there is no available gauging system to measure the actual PSI. For optimum inflation each patient needs the use, each and every time, of a computerized pressure mapping equipment. This equipment is available in certain facilities however is basically used for initial wheelchair seating assessments. Another drawback of this system is that the entrapped air becomes uncomfortably hot and this leads to a loss of tissue integrity. When these types of cushions are over inflated or under inflated they become extremely unstable bases for pelvic posturing. Additionally, these cushions are prone to puncturing.
Another category of commonly seen wheelchair cushion employs a contoured foam base encased within a cover. The foam base may comprise the entire cushion or it may utilize additional pressure relieving media disposed on top of its contoured foam base. This contoured foam base may be a xe2x80x9cdeformingxe2x80x9d foam, i.e., compresses under normal loading conditions, or a xe2x80x9cnon-deformingxe2x80x9d foam, i.e., a rigid foam. One popular model of a contoured base cushion uses a liquid gel or fluid in two or three separate compartments disposed on top of a contoured rigid foam base. This type of cushion suffers from the fact that when loaded, the gel migrates to the perimeter of the each of the encapsulating envelopes. Once the gel has migrated away from the areas corresponding to the bony prominences (coccyx, sacrum or ischial tuberosities) the entire device becomes ineffective as its rigid foam base offers little protection (pressure reduction) or actually promotes pressure sore development. Additionally, the fluid or gel itself tends to separate into its components and must be regularly kneaded to maintain a proper operating viscosity. Efforts to lighten gel filled cushions by lightening the gel has resulted in gels which more rapidly separate. Fluid gel cushions also have the disadvantage of being subject to freezing in cold climates.
Another type of cushion in the contoured base category utilizes an inflatable air bladder disposed on top of a contoured pressure-relieving foam base. This type of cushion usually has interconnected vertical air cells of the type previously cited in the Roho cushion. In a contoured foam base application these interconnected air cells are generally of a reduced height. This reduction in the height of the air cells represents an improvement with regard to patient stability. These cushions become equally hot with sustained use and remain vulnerable to puncture and still require almost daily adjustment of the pressure of the contained volume of air.
Another type of contoured foam base cushion uses a molded pressure relieving foam base in conjunction with a solid elasticized urethane gel interface. The type of elasticized urethane gel most commonly employed is comprised of long chain molecules derived from isocyanates and polyols. These cushions provide very high pressure reduction and afford significantly enhanced postural alignment and stability. The solid gel contoured foam base cushion requires no maintenance by either the user or caregiver and offers a stable platform for superior pelvic positioning. The solid elastomeric gel remains uniform, with minimal migration, at loaded equilibrium. The solid urethane gel also represents an improvement in providing the lowest sustained interface temperatures. The main drawback to this type of cushion is that they are very heavy. Frequently, this type of cushion, although providing the required pressure relief and stability, is eliminated from consideration by the patient and therapist alike, because the patient or an elderly spouse can not easily manage the cushion""s weight. In the course of frequent daily activities, the cushion must be removed from the wheelchair prior to the wheelchair being folded for transportation. Frequently, the wheelchair user must retrieve their cushion from a car seat prior to transferring back into the wheelchair. Many elderly wheelchair users must follow this routine as they do not meet the necessary funding criteria to obtain a power wheelchair. Additionally the design convention for these types of cushions is to use a relatively firm foam in the contoured base. These cushions are expensive, and a firmer foam is selected for its resistance to assume any permanently compressed shapes. Although this design strategy improves the cushions useable life, it diminishes the cushions ability to additionally conform beyond the manufactured contours to the individual user.
Another type of cushion is the compression bonded urethane matrix or honeycomb cushion. This type of cushion uses two strata of a flexible urethane matrix which form a network of regularly shaped cells. In some models one of the strata is contoured. The upper extremity of the upper strata is open and the cushion relieves pressure via the distortion of the open cell walls mostly at the patient interface. This type of cushion is very low in weight, but tends to be less comfortable. These cushions have little ability to additionally conform to the individual patient""s anatomy beyond this region of upper cell wall distortion. Although flexible in all three dimensions, these cushions assume the general shape of the wheelchair sling upholstery because the upper strata cannot flex within the confines of the lower strata.
It would be desirable to provide a cushion structure which combines the best characteristics of pressure reduction, stable positioning, light weight and cool patient interface.
An anatomical support according to the present invention includes a patient interface layer of gel, a matrix panel and a foam base.
In a preferred form the gel is a solid gel bonded to the matrix panel in a reactive molding process to form a gel matrix composite panel. In one embodiment, the foam base includes multiple layers of foam of different densities. The base may include a contoured layer, which layer generates a contoured surface at the patient interface.
In another embodiment, the present invention is a wheelchair cushion having a contoured base which includes a pommel or abductor formed from foams of differing densities to be more resilient in the front to back horizontal direction than in the side-to-side direction.